1. Field of the Invention
This invention relates generally to endless power transmission belts and, more particularly, to improved belts having enhanced noise suppression capability. Specifically, the present invention relates to an improved endless belt in the form of a v-ribbed belt having an elastomeric composition including means for mitigating unstable frictional behavior of the belt in order to suppress noise generation and reduce pilling.
2. Description of the Prior Art
Many current automotive accessory drive systems employ a multi-ribbed v-belt to transmit power from the engine to the accessories. Most v-belt constructions associated with this application, as well as other endless belts such as power transmission belts, micro-ribbed belts, and the like, typically utilize neoprene, SBR, or polybutadiene-based polymer systems incorporating a variety of additives to enhance certain performance features. One performance characteristic of these belts which has become increasingly important to automotive original equipment and aftermarket applications over the past few years is that of quiet belt operation.
Examples of power transmission belts, v-belts, and micro-ribbed belts are disclosed in U.S. Pat. Nos. 3,138,962; 3,200,180; 4,330,287; and 4,332,576. Examples of formation of such belts are readily disclosed in U.S. Pat. No. 3,200,180 as indicated above and U.S. Pat. Nos. 3,772,928 and 4,066,732. These patent references are merely examples of the types of belts and state-of-the-art formation techniques thereof.
Under certain belt and drive conditions, multi-ribbed v-belts can exhibit an audible chirping or squealing noise. One solution to the noise problem in such belts has been to reduce the coefficient of friction of the sprocket engaging surface of the belt by isolating or removing as much of the elastomer as possible from near the surface of the belt when it comes in contact with sprocket teeth or flanges. Such an approach is taken in U.S. Pat. No. 3,772,929. Another manner of dealing with the noise generation problem is disclosed in U.S. Pat. No. 3,964,328 wherein a layer of elastomer impervious material is utilized during the casting operation and bonded to one side of a wear-resistant fabric.
Another approach taken to reduce noise generation in such belts has been to incorporate certain types of short length textile fibers into the belt undercord stock. This practice has been used not only to help inhibit noise but also to enhance wear properties. For particularly demanding belt applications, higher concentrations of textile fiber have been frequently required to ensure acceptable belt noise performance. However, difficulties have often been encountered in the mixing process when a large amount of fiber is to be dispersed into the rubber stock. Consequently, proper dispersion has usually required multiple passes through the mixer which is both time consuming and costly. Furthermore, large quantities of fiber incorporated into the rubber stock have been shown to be detrimental to certain other belt performance characteristics such as fatigue life.
Another problem experienced by multi v-ribbed belts is that of pilling, i.e., wear resulting in the formation of small balls of elastomer material between the ribs of the belt. Pilling can be a source of warranty problems from appearances as well as create noise and tracking problems. Belts to date have not yet effectively addressed this problem.
Consequently, there remains a need to produce a multi-ribbed or v-belt which is quiet during belt operation, reduces pilling and includes a noise suppression mechanism throughout the life of the belt even as it wears, yet does not affect other belt performance characteristics such as fatigue life, temperature resistance, and the like.